I suppose he is indicating a new role for her - from being barren to being the mother of nations. Now she is royalty. Sarah and her husband are starting a new dynasty. Isaac, Sarah's firstborn son (but not Abraham's firstborn son), is the proof that God's promises of land and descendants are true. God has proven himself in a most spectacular way. What other 90-year-old woman has given birth?
So we see what an important role Sarah had in God's plan. Indeed, she was essential, as was Mary the mother of Jesus.
We have two reflection questions today: What is my role in God's plan? What name does God call me?
Let us pray. God, you called Sarah to a new role, even in her old age. Please allow me to serve you, even to the last day of my life.